Department of Nuclear Engineeringhttp://hdl.handle.net/1721.1/7852
Fri, 09 Dec 2016 17:28:58 GMT2016-12-09T17:28:58ZA review of the MITR-II basis accidenthttp://hdl.handle.net/1721.1/104158
A review of the MITR-II basis accident
McCauley, John Jay
Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE; Includes bibliographical references.
Fri, 01 Jan 1982 00:00:00 GMThttp://hdl.handle.net/1721.1/1041581982-01-01T00:00:00ZApplication of advanced fuel concepts for use in innovative pressurized water reactorshttp://hdl.handle.net/1721.1/103733
Application of advanced fuel concepts for use in innovative pressurized water reactors
Andrews, Nathan Christopher
This work addresses several specific knowledge gaps that exist in the use of alternative fuel and cladding combinations in a pressurized water reactor (PWR) environment. In the switch from a UO2 with zirconium-based cladding to any other combination, there is a multitude of questions that need to be answered. This work examines three of these knowledge gaps: (1) the disposition of weapons-grade plutonium in thorium and silicon carbide cladding, (2) economics of accident tolerant fuel (ATF) claddings and (3) breeding of plutonium in uranium nitride fuel. Burning weapons-grade plutonium in a standard pressurized water reactor (PWR) using thoria as a fuel matrix has been compared to using urania. Two cladding options were considered: a 0.76 mm thick silicon carbide ceramic matrix composite (SiC CMC) and 0.57 mm thick standard Zircaloy cladding. A large benefit was found in using thoria compared to urania in terms of plutonium percentage and mass burned. A slightly smaller mass of plutonium is required in a core with SiC CMC cladding, due to its lower neutron absorption compared to Zircaloy. The thorium system was also better from a non-proliferation viewpoint, resulting in less fissile mass at discharge and more fissile mass burned over an assembly's lifetime. A limited safety comparison was made for two reactivity insertion accidents: (1) highest worth rod ejection accident (REA) and (2) main steam line break (MSLB). The MSLB accident demonstrated a safe value for the minimum departure from nucleate boiling ratio. The maximum enthalpy added to the fuel during the REA was also below current regulatory limits for PWRs. This indicates that the more negative moderator temperature coefficients of thoria-plutonia and urania-plutonia fuel, compared to a typical PWR design, were not limiting. For an ATF cladding to replace zirconium alloys, it must be economically viable by having similar fuel cycle costs to today's materials. Four proposed materials are examined: stainless steel (SS), FeCrAl alloy, molybdenum (Mo) and SiC CMC, each having its own development time and costs. The chosen cladding thicknesses were dependent on strength and manufacturing constraints. It was found that all options may end up requiring higher enrichment than zirconium-based claddings for the same fuel cycle length. If the present value of avoiding a reactor accident with a large radioactivity release is estimated using past experience for LWR large accidents and if it is assumed that ATF cladding is able to prevent such release, there is a definite net economic benefit relative to typical Zircaloy cladding only in using SiC, since it only results in a small fuel cycle cost increase. There is only a marginal benefit in using SiC to prevent a core-only loss without radioactivity release (TMI-type) accident and a large loss using metallic ATF concepts. The thermal hydraulic and neutronic feasibility of a nitride fueled pressurized water reactor (PWR) breeder design were examined. Because of its higher fuel density, nitride fuel would be preferable to traditional oxide fuel in attempting to achieve breeding in a PWR. The design chosen uses large hexagonal assemblies with 14 inner seed pin rows and 4 outer blanket pin rows. In this design, reactor grade plutonium of 12.75 wtHM was used as fuel. Nitride was also simulated as being 100% N-15, to limit neutronic penalties and C-14 production. The as specified assembly model only achieved a fissile inventory ratio (FIR) value above 1.0 when the thimble regions were assumed to be voided, which lowers the H/HM ratio in the assembly. This led to FIR values above 1.0 for the oxide, 85% theoretical density nitride (N85) and 95% theoretical density nitride (N95). All were at an FIR of 1.03 at 35 MWd/kgHM. However, the single batch discharge burnup of the voided assembly in MWd/kgHM was 32.2 for N95, 24.5 for N85, while only 15.6 for the oxide.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 198-202).
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/1721.1/1037332015-01-01T00:00:00ZExperimental study of plasma transport using X-ray imaging spectroscopy in Alcator C-Modhttp://hdl.handle.net/1721.1/103732
Experimental study of plasma transport using X-ray imaging spectroscopy in Alcator C-Mod
Gao, Chi, Ph. D. Massachusetts Institute of Technology
The high resolution X-ray spectrometer with spatial resolution (HiReX-Sr) is intensively used in the studies of impurity, momentum and energy transport in Alcator C-Mod. This thesis investigates three phenomena using HiReX-Sr: (1) Non-local heat transport (the breakdown of a local expression for the heat flux) is observed in linear Ohmic confinement (LOC) regime plasmas in cold pulse injection experiments. This effect disappears in saturated Ohmic confinement (SOC) regime plasmas. The plasma rotation reverses direction across this transition. Transport analysis show that a transient internal transport barrier (ITB) forms in the core plasma. Cold pulse modulation experiments suggest a non-diffusive heat transport behavior. The change of dominant turbulence mode from electron mode dominance in LOC plasmas to ion mode dominance in SOC plasmas is proposed to be the underlying mechanism for the correlations among the disappearance of the non-local effect, the rotation reversals and the LOC/SOC transitions. This work extends the understanding of non-local phenomena in the tokamak plasmas. (2) Evidence of inward momentum pinch in ICRF modulation experiments. The momentum transport coefficients are calculated based on a simplified model. It is found that within 0.1 < r/a < 0.5, the momentum diffusivity is lower than the ion thermal diffusivity and the momentum pinch is inward. (3) ICRF induced argon pumpout in hydrogen-deuterium plasma is observed in Alcator C-Mod when the H-to-D level is relatively high (nH/nD ~ 35% - 50%). The pumpout effect is maximal when nH/nD ~ 40% ± 5%, at which level the hydrogen-deuterium hybrid layer is close to the Ar16+ 2nd harmonic resonant layer. This suggests that the pumpout of argon could be due to the energy absorbed from the enhanced left-hand polarized electric field through 2nd harmonic resonance. Further experiments are proposed to verify this impurity-wave interaction mechanism, which is potentially useful for active impurity control in fusion devices. Thesis Supervisor: Dr. John E. Rice
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 217-239).
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/1721.1/1037322015-01-01T00:00:00ZQuantum control of spin systems in diamondhttp://hdl.handle.net/1721.1/103731
Quantum control of spin systems in diamond
Hirose, Masashi, Ph. D. Massachusetts Institute of Technology
The precise control of a system which behaves according to the principles of quantum mechanics is an essential task in order to fully harness the unique properties of quantum mechanics, such as superposition and entanglement, for practical applications. Leveraging the quantum nature of the system would enable, for example, the implementation of quantum computation and quantum metrology. However, any realistic quantum system is inevitably coupled to its environment. The interaction with its surroundings irrevocably destroys the quantum nature of the system: mitigating decoherence is thus one of the central problems in quantum control. In this thesis, we develop novel control methods to protect a qubit from decoherence by two distinct approaches, and demonstrate them experimentally using the nitrogen-vacancy (NV) center in diamond. The first approach rests on an open-loop control scheme and is tailored to improve quantum sensing tasks. We develop a continuous dynamical decoupling (CoDD) method that allows us to tune the degree of protection from a dephasing environment. Exploiting this flexibility, we show that the CoDD can be used to measure magnetic fields with sensitivity comparable to existing methods, while providing superior versatility in practical experimental settings. This protocol can adapt to various sensing conditions that might occur in biological and materials science such as measurement time and sensitive frequency. The second approach exploits a coherent feedback protocol. We take advantage of a long-lived nuclear spin as an ancillary spin to protect the qubit of interest from decoherence. We show that the protocol protects the qubit as long as open-loop dynamical decoupling control schemes and it can be used against more general types of noise than the open-loop protocol. This method thus offers an alternative protocol to protect the qubit from decoherence in quantum computation and quantum metrology.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 101-113).
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/1721.1/1037312015-01-01T00:00:00Z